Abstract

In Windows imaging applications, the most used API for scanning is TWAIN www.twain.org.
Unfortunately, the new .NET Framework has no built-in support for TWAIN. So we have to work with the interop methods of .NET to
access this API. This article doesn't explain this interop techniques, and good knowledge of the
TWAIN 1.9 specifications is assumed! The sample code included doesn't present a
finished library, only some essential steps for a minimal TWAIN adaption to .NET applications.

Details

First step was to port the most important parts of TWAIN.H, these are found in TwainDefs.cs. The real logic for
calling TWAIN is coded in the class Twain, in file TwainLib.cs.. As the TWAIN API is exposed by the Windows
DLL, twain_32.dll, we have to use the .NET DllImport mechanism for interop with legacy code. This DLL has the
central DSM_Entry(), ordinal #1 function exported as the entry point to TWAIN. This call has numerous parameters,
and the last one is of variable type! It was found to be best if we declare multiple variants of the call like:

For some sort of 'callbacks', TWAIN uses special Windows messages, and these must be caught from the application-message-loop.
In .NET, the only way found was IMessageFilter.PreFilterMessage(), and this filter has to be activated with a call
like Application.AddMessageFilter(). Within the filter method, we have to forward each message to
Twain.PassMessage(), and we get a hint (enum TwainCommand) back for how we have to react.

Sample App

The sample is a Windows Forms MDI-style application. It has the two TWAIN-related menu items Select Source... and
Acquire... Once an image is scanned in, we can save it to a file in any of the GDI+ supported file formats (BMP, GIF,
TIFF, JPEG...)

Limitations

All code was only tested on Windows 2000SP2, with an Epson Perfection USB scanner and an Olympus digital photo camera. The
scanned picture is (by TWAIN spec) a Windows DIB, and the sample code has VERY little checking against error return codes and
bitmap formats. Unfortunately, no direct method is available in .NET to convert a DIB to the managed Bitmap class... Some known
problems may show up with color palettes and menus.

Comments and Discussions

I have been using the Leadtools Twain interface for a variety of scanners. We don't want the dialog from the driver to display unless requested. I have one scanner driver that will not scan unless the dialog is displayed.

I downloaded your code and it works well if the dialog is displayed. Any ideas on how to just do the scan with no dialog?

2) How to perform automatic scanning of image when placing an ID card in the ID scanner device?

3) How to perform Scanning operation for the Front and Back side of ID card?

4) How to perform Scanning of UV( Ultraviolet) and IR(Infrared) type ID Cards?

5) After scanning the images how to edit feature's like Calibrate, Resolution, Height, Width, Color, Image Brightness, Image Contrast, Invert Images? If so by which method and parameters can be applied?

2) How to perform automatic scanning of image when placing an ID card in the ID scanner device?

3) How to perform Scanning operation for the Front and Back side of ID card?

4) How to perform Scanning of UV( Ultraviolet) and IR(Infrared) type ID Cards?

5) After scanning the images how to edit feature's like Calibrate, Resolution, Height, Width, Color, Image Brightness, Image Contrast, Invert Images? If so by which method and parameters can be applied?

I read ur article and its really useful for me but . When I run ur application Press Acquire button from menu strip new form comes for Scan Properties. Right now Im stuck with disable the second Scan property form because I need press acquire button and just start scanning.

Having a error with TwainLib.Twain.DSMident(TwainLib.TwIdentity, IntPtr, TwainLib.TwDG, TwainLib.TwDAT, TwainLib.TwMSG, TwainLib.TwIdentity)
on windows 8.1 professional - comes up with a System.AccessViolationException Exception

has anyone seen this before and is a way to resolve

The application in C# is complied to a 32 bit target with framework 4.0 and vb studio 2013
the same exact error occurs with teh demo application from this site

That did work - thank you
I am running into another issue though - the app is now freezing at the following command
rc = DSMident(appid, IntPtr.Zero, TwDG.Control, TwDAT.Identity, TwMSG.OpenDS, srcds);

do you see anything wrong with that - is OpenDS supported on windows 8.1

First of all just want to thanks to the author.
I have accomplished my project (Document Management System) after modifying some parts of the code.
But i have 1 problem encountered, can you help me figure out the error below:

"Insufficient Memory. (Code: DS41001)"

OS : Windows XP
Scanner : Fujitsu (fi 6230-z)

The error occurs usually on the middle of scanning or when i resume my scan after adding paper.